The present invention relates generally to building construction and reinforcement, and specifically to a continuity system that resists tension from wind uplift forces or overturning forces from wind or seismic events while compensating for the downward settling of buildings caused by shrinkage of wooden members. Most specifically, the present invention relates to a ratcheting take-up device that reduces slack due to wood shrinkage and building settling in a holdown system of continuous rods, eases installation and compensates for imperfectly aligned rods.
A continuity system is a secondary support system that ties walls or other building elements together and resists lateral overturning forces or uplift forces from events such as earthquakes or strong winds. Earthquake and wind forces produce overturning and uplift loads in the building, which load the building elements in overturning or uplift with respect to the building foundation. A continuity system resists such movements of the building elements. A continuity system generally comprises a plurality of interconnected vertically-oriented elements, typically metal rods and bearing plates, or holdowns, that provide a discrete structural mechanism or load path framework for the transfer of loads through the building from the structural elements that are intended to resist such forces, such as roof or floor diaphragms and shearwalls, to the continuity system, and then to the foundation. For example, the presence of a continuity system enables wall panels to resist overturning and/or moments that might damage or destroy the wall.
A known continuity system is described in U.S. Pat. No. 4,875,314 (“the '314 patent”), the entire disclosure of which is hereby incorporated herein by reference. The '314 patent describes a system in which at least one tie rod is connected to the foundation through a simple threaded coupler and a foundation anchor. Although the tie rod system can be used in a single-story structure, it is particularly suited to multistory structures, as illustrated in the '314 patent. In a multistory structure, a series of anchor elements is used to couple multiple tie rods in a line from the foundation to the top plate of the top story of the structure. The anchor elements of the '314 patent, in addition to coupling tie rods together, are used to secure the tie rods at each level of the structure to eliminate initial slack in the system. The principal shortcoming of the system of the '314 patent is the lack of a means of compensating for slack that builds up in the system as the wood structural members shrink over time. As slack builds up in the system, the system's capacity to resist uplift is correspondingly reduced.
The prior art includes a number of technical solutions to the problem of increasing slack in continuity systems. Simpson Strong-Tie Company's Anchor Tiedown System uses the TUD and ATUD take-up devices, as well as the CTUD coupling take-up device. The CTUD coupling take-up device is the subject of U.S. Pat. No. 7,905,066, granted to Steven E. Pryor et al. All three devices are driven by a torsion spring. The TUD and ATUD are slipped over the tie rod between a horizontally disposed member and a nut threaded onto the tie rod, and they expand to fill the space as it expands enlarges. The CTUD threads onto and couples the vertically-aligned ends of two tie rods, drawing the two together to maintain tight connections between the wood and steel elements as the wood structural members shrink over time.
Similar continuity systems with ratcheting take-up devices are described in U.S. Pat. No. 6,007,284 the entire disclosure of which is hereby incorporated herein by reference, and U.S. Pat. No. 7,744,322, the entire disclosure of which is also hereby incorporated herein by reference. These devices, while similar in both basic form and function to the present invention, lack inventive features of the present invention.
The ratcheting take-up device of the present invention eases installation of continuity systems, compensates for tie rods that are not perfectly perpendicular to the top and bottom plates, and takes up slack in the continuity system after installation.